Method for flushing an exhaust-gas cleaning system

ABSTRACT

A method for flushing an exhaust-gas cleaning system of an internal combustion engine having a catalytic converter with at least one catalyst bed, whereby an exhaust gas from the internal combustion engine is supplied to the exhaust-gas cleaning system in an active operating phase of the exhaust-gas cleaning system, and no exhaust gas is supplied to the exhaust-gas cleaning system in a passive operating phase of the exhaust-gas cleaning system, whereby a temperature of the at least one catalyst bed is determined and the flushing is performed depending on the determined temperature, whereby the exhaust-gas cleaning system is flushed in the passive operating phase of the exhaust-gas cleaning system by a flushing device, which is connected directly to an exhaust-gas line.

BACKGROUND OF THE INVENTION

Embodiments of the invention relate to a method for flushing an exhaust-gas cleaning system of an internal combustion engine comprising a catalytic converter with at least one catalyst bed, whereby an exhaust gas from the internal combustion engine is supplied to the exhaust-gas cleaning system in an active operating phase of the exhaust-gas cleaning system and no exhaust gas is supplied to the exhaust-gas cleaning system in a passive operating phase of the exhaust-gas cleaning system, whereby a temperature of the at least one catalyst bed is determined and the flushing is performed depending on the determined temperature.

Methods for flushing a catalytic converter installed in an exhaust-gas cleaning system of an internal combustion engine with at least one catalyst bed are already known in order to cool a catalyst bed that is too strongly heated during the operation of the internal combustion engine, so as to prevent overheating and associated damage to the catalyst bed (e.g. DE 2401287, EP 1033480 A1).

Experiments by the applicant have shown that, after shutting down an internal combustion engine, e.g. a stationary reciprocating-piston gas engine, the exhaust-gas temperature downstream of an exhaust-gas turbine of a turbocharger can increase to more than 400° C. This increase in the exhaust-gas temperature leads to heating of a catalytic converter arranged in the exhaust-gas cleaning system. If the internal combustion engine is then to be restarted but suffers a false start, then the exhaust-gas lines and thus also the exhaust-gas cleaning system together with the catalytic converter are filled with a fuel-gas/air mixture. Depending on the temperature of the catalyst bed of the catalytic converter and the number of unsuccessful start attempts in series, undesirable oxidation of the fuel gas can occur, which can lead to damage to the catalytic converter and, in the worst case, even to a deflagration.

BRIEF DESCRIPTION OF THE INVENTION

The object of embodiments of the invention is therefore to provide an improved method, improved in comparison with the prior art, for flushing an exhaust-gas cleaning system of an internal combustion engine comprising a catalytic converter with at least one catalyst bed, by means of which a safer start-up of the internal combustion engine can be achieved.

This object is achieved according to embodiments of the invention by a method for flushing an exhaust-gas cleaning system of an internal combustion engine comprising a catalytic converter with at least one catalyst bed, wherein an exhaust gas from the internal combustion engine is supplied to the exhaust-gas cleaning system in an active operating phase of the exhaust-gas cleaning system, and no exhaust gas is supplied to the exhaust-gas cleaning system in a passive operating phase of the exhaust-gas cleaning system, wherein a temperature of the at least one catalyst bed is determined and the flushing is performed depending on the determined temperature, wherein the exhaust-gas cleaning system is flushed in the passive operating phase of the exhaust-gas cleaning system by a flushing device, which is connected directly to an exhaust-gas line. Embodiments of the invention are defined in the dependent claims.

According to embodiments of the invention, it is thus provided that the exhaust-gas cleaning system is flushed in the passive operating phase of the exhaust-gas cleaning system.

With regard to the exhaust-gas cleaning system, in principle two types of operating phases are distinguished. An active operating phase of the exhaust-gas cleaning system is characterized in that an exhaust gas from the internal combustion engine is fed into the exhaust-gas cleaning system. A passive operating phase of the exhaust-gas cleaning system is characterized in that no exhaust gas is fed into the exhaust-gas cleaning system. During the ongoing operation of an internal combustion engine, during which the exhaust-gas cleaning system is supplied with an exhaust gas from the internal combustion engine, the exhaust-gas cleaning system is thus in an active operating phase.

By flushing the exhaust-gas cleaning system in a passive operating phase of the exhaust-gas cleaning system, an influence on the exhaust-gas cleaning system can also be exerted outside of an active operating phase of the exhaust-gas cleaning system. In particular, the overheating of the catalytic converter or its catalyst beds can be prevented after the shutdown of an internal combustion engine or before the start-up of an internal combustion engine after previous false starts.

A flushing of the exhaust-gas cleaning system can be performed by a flushing device, which has its own drive. This has the significant advantage that the flushing of the exhaust-gas cleaning system can be performed independently of the operating state of the internal combustion engine. This also makes it possible to perform a flushing operation when the internal combustion engine is in a passive operating state. Furthermore, the disadvantages, such as when using an electric turbocharger as a flushing device, which forcibly cools the internal combustion engine, are thereby eliminated. Since only the exhaust-gas cleaning system is flushed by a separately driven flushing device and thus also cooled, no undesirable cooling of the internal combustion engine occurs. Such a separate drive of the flushing device can be designed e.g. as an electric motor.

In an embodiment, it can be provided that the exhaust-gas cleaning system is flushed only in the passive operating phase of the exhaust-gas cleaning system. In other words, the exhaust-gas cleaning system is flushed exclusively in the passive operating phases of the exhaust-gas cleaning system, in which no exhaust gas is fed into the exhaust-gas cleaning system.

It can, in an embodiment, be provided that the temperature of the at least one catalyst bed is determined in the passive operating phase of the exhaust-gas cleaning system.

According to an embodiment, it can be provided that the exhaust-gas cleaning system is flushed after a shutdown of the internal combustion engine. As a result, a combustible fuel/air mixture which is still present in the exhaust tract is removed from the exhaust tract before restarting the internal combustion engine.

A particular embodiment variant provides that a period of time is determined depending on the determined temperature, during which the exhaust-gas cleaning system is flushed. In determining the period of time, it can be considered that, in the case of a hot catalyst or catalyst bed, it must be flushed for a longer time than in the case of a colder catalyst or catalyst bed, so as to ensure that no combustible fuel/air mixture is still present in the exhaust tract.

According to an embodiment, it can be provided that the exhaust-gas cleaning system is flushed after a start-up of the internal combustion engine. In this way, it can be ensured that, when the internal combustion engine is started up, there is no longer any combustible fuel/air mixture present which can damage the catalytic converter due to undesirable oxidation in the catalytic converter.

It has been found to be particularly advantageous that the exhaust-gas cleaning system is flushed until the temperature of the at least one catalyst bed is lower than or equal to a predetermined setpoint temperature. The predetermined setpoint temperature can thus, in an embodiment, be selected such that, below the predetermined setpoint temperature, no significant risk arises from the catalytic converter serving as ignition source. Depending on the dimensioning of the catalytic converter and the fuel-gas quality used, the predetermined setpoint temperature can be in a range from around 200° C. to around 400° C., for example around 300° C.

It can thus be provided that the exhaust-gas cleaning system is flushed if the temperature of the at least one catalyst bed before flushing is higher than or equal to a predetermined threshold value. The predetermined threshold value can thus, in an embodiment, be selected such that, below the predetermined threshold value, no significant risk arises from the catalytic converter serving as ignition source. Depending on the dimensioning of the catalytic converter, the predetermined threshold value can be in a range from around 200° C. to around 400° C., for example around 300° C.

In the event that the temperature of the at least one catalyst bed is lower than the predetermined threshold value, it can be provided that a so-called safety flush occurs for a predetermined period of time, which may be in a range from around 30 seconds to around 225 seconds, depending on the size of the exhaust tract.

In an embodiment, it can be provided that a first exhaust-gas temperature value is determined upstream of the catalytic converter and a second exhaust-gas temperature value is determined downstream of the catalytic converter, whereby the temperature of the at least one catalyst bed is determined by taking account of the first exhaust-gas temperature value and the second exhaust-gas temperature value.

In an embodiment, it can be provided that the exhaust-gas cleaning system is flushed with air.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and advantages of this invention are explained in more detail below in the description of the figures, with reference to the exemplary embodiments shown in the drawings. The figures show the following:

FIG. 1 shows an internal combustion engine with an exhaust-gas cleaning system,

FIG. 2 shows a flowchart relating to the flushing of an exhaust-gas cleaning system after the shutdown of an internal combustion engine,

FIG. 3 shows a flowchart relating to the flushing of an exhaust-gas cleaning system before the start-up of an internal combustion engine.

DETAILED DESCRIPTION

FIG. 1 shows an internal combustion engine 4, in the exhaust-gas line 5 of which an exhaust-gas cleaning system 3 is arranged. The internal combustion engine 4 in this example is a stationary gas engine, which is operated with a fuel-gas/air mixture. The exhaust-gas cleaning system 3 comprises a catalytic converter 1, which in this example is equipped with two catalyst beds 2. Upstream of the exhaust-gas cleaning system 3, a flushing device 6 is arranged, through which the air L can be introduced into the exhaust-gas line 5 upstream of the exhaust-gas cleaning system 3 in order to flush the exhaust-gas cleaning system 3.

According to the proposed method, the exhaust-gas cleaning system 3 is flushed depending on a determined temperature T of the catalyst beds 2 of the catalytic converter 1. To determine the temperature T in this example, two temperature sensors 7, 8 are arranged upstream and downstream of the exhaust-gas cleaning system 3. The temperature sensors 7, 8 determine the temperature of the exhaust gas of the internal combustion engine 4. The temperature sensor 7 detects a first exhaust-gas temperature value T1 upstream of the catalytic converter 1, and the temperature sensor 8 determines a second exhaust-gas temperature value T2 downstream of the catalytic converter 1. The determined exhaust-gas temperature values T1, T2 are reported via signal lines 10 to a control device 9, which determines an estimated temperature T of the catalyst beds 2 from the first exhaust-gas temperature value T1 and the second exhaust-gas temperature value T2. This determination of the temperature T of the catalyst beds 2 can be performed e.g. by calculating the arithmetic mean of the first exhaust-gas temperature value T1 and the second exhaust-gas temperature value T2, or e.g. further calculations are performed, taking into account the caloric influencing variables, the response times of the measurement signal chains and the operating history. Depending on the determined temperature T, the control device 9 can activate the flushing device 6 via a control line 11 in order to introduce air L upstream of the exhaust-gas cleaning system 3 into the exhaust-gas line 5, thereby flushing the exhaust-gas cleaning system 3.

FIG. 2 shows, by way of example, a flowchart relating to the flushing of the exhaust-gas cleaning system 3 after the shutdown of an internal combustion engine 4. Starting from step S1, in which the internal combustion engine runs and supplies exhaust gas to the exhaust-gas cleaning system 3, whereby the exhaust-gas cleaning system 3 is in an active operating phase, a stop command for stopping the internal combustion engine 4 is initiated in step S2. Accordingly, the internal combustion engine 4 is stopped in step S3. As a result, no further exhaust gas from the internal combustion engine 4 is fed into the exhaust-gas cleaning system 3, and the exhaust-gas cleaning system 3 is in a passive operating phase in step S4. In this passive operating phase of the exhaust-gas cleaning system 3, the temperature T of the at least one catalyst bed 2 of the catalytic converter 1 of the exhaust-gas cleaning system 3 is now determined in step S5. In step S6, a period of time tp is determined depending on the determined temperature T of the at least one catalyst bed 2, during which the exhaust-gas cleaning system 3 is flushed in step S7.

FIG. 3 shows, by way of example, a flowchart for the flushing of the exhaust-gas cleaning system 3 before the start-up of an internal combustion engine 4. In step S8, a passive operating phase of the exhaust-gas cleaning system 3 is then assumed, which may be caused by the fact that the internal combustion engine 4 is not running. In step S9, the start command for starting the internal combustion engine 4 is executed. In step S10, it is checked whether the start command was preceded by a false start of the internal combustion engine 4, or whether the internal combustion engine 4 was previously shut down (e.g. within a predefined period). If a false start has not occurred and the internal combustion engine 4 was not shut down recently, the temperature T of the at least one catalyst bed 2 of the catalytic converter 1 of the exhaust-gas cleaning system 3 is determined in step S11. In step S12, it is checked whether the determined temperature T of the at least one catalyst bed 2 is lower than or equal to a setpoint temperature value TS. If this is not the case and the temperature T is higher than the setpoint temperature value TS, then the exhaust-gas cleaning system 3 is flushed in step S13, and in step S11 the determination of the temperature T of the at least one catalyst bed 2 is continued. If it is found in step S12 that the temperature T of the at least one catalyst bed 2 is lower than or equal to the setpoint temperature TS, then the internal combustion engine 4 can be started in step S14. By starting the internal combustion engine 4, an exhaust gas from the internal combustion engine 4 is fed into the exhaust-gas cleaning system 3, and the exhaust-gas cleaning system 3 is in an active operating phase in step S15.

If it is determined in step S10 that a false start of the internal combustion engine 4 has previously occurred, or the internal combustion engine 4 was shut down recently, the temperature T of the at least one catalyst bed 2 is determined in step S16, and in step 17 it is checked whether the temperature T of the at least one catalyst bed 2 is higher than or equal to a threshold value TT. If this is the case and thus the temperature T is higher than or equal to the threshold value TT, then we continue in step S12. If this is not the case and thus the temperature T is lower than the threshold value TT, then a safety flush of the exhaust-gas cleaning system 3 is performed in step S18. The exhaust-gas cleaning system 3 can thus be flushed for a fixed predetermined duration of e.g. 30 to 225 seconds, depending on the size of the exhaust tract. After this safety flush in step S18, step S14 (starting of the internal combustion engine 4) is continued.

This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A method for flushing an exhaust-gas cleaning system of an internal combustion engine comprising a catalytic converter with at least one catalyst bed, wherein an exhaust gas from the internal combustion engine is supplied to the exhaust-gas cleaning system in an active operating phase of the exhaust-gas cleaning system, and no exhaust gas is supplied to the exhaust-gas cleaning system in a passive operating phase of the exhaust-gas cleaning system, wherein a temperature of the at least one catalyst bed is determined and the flushing is performed depending on the determined temperature, wherein the exhaust-gas cleaning system is flushed in the passive operating phase of the exhaust-gas cleaning system by a flushing device, which is connected directly to an exhaust-gas line.
 2. The method according to claim 1, wherein the exhaust-gas cleaning system is flushed only in the passive operating phase of the exhaust-gas cleaning system.
 3. The method according to claim 1, wherein the temperature of the at least one catalyst bed is determined in the passive operating phase of the exhaust-gas cleaning system.
 4. The method according to claim 1, wherein the exhaust-gas cleaning system is flushed after a shutdown of the internal combustion engine.
 5. The method according to claim 1, wherein a period of time during which the exhaust-gas cleaning system is flushed is determined depending on the determined temperature.
 6. The method according to claim 1, wherein the exhaust-gas cleaning system is flushed before a start-up of the internal combustion engine.
 7. The method according to claim 1, wherein the exhaust-gas cleaning system is flushed until the temperature of the at least one catalyst bed is lower than or equal to a predetermined setpoint temperature.
 8. The method according to claim 7, wherein the exhaust-gas cleaning system is flushed if the temperature of the at least one catalyst bed before flushing is higher than or equal to a predetermined threshold value E.
 9. The method according to claim 1, wherein a first exhaust-gas temperature value is determined upstream of the catalytic converter and a second exhaust-gas temperature value is determined downstream of the catalytic converter, wherein the temperature of the at least one catalyst bed is determined by taking account of the first exhaust-gas temperature value and the second exhaust-gas temperature value. 